We propose new solid-state NMR experiments to determine the structure and dynamics of protein complexes which are unsuited for diffraction studies and too big for solution-state NMR. The versatile rotational- echo, double-resonance (REDOR) and transferred-echo, double-resonance (TEDOR) analytical methods that we have developed in the last four years for the accurate determination of internuclear distances (and hence geometry and structure), and proposed new combined TEDOR-REDOR and TEDOR-TEDOR experiments, are heteronuclear NMR techniques that are directly applicable to the characterization of protein complexes. These complexes can be examined either as polycrystalline materials in contact with mother liquor, or as freeze-quenched lyophilized solids embedded in cryoprotectant buffer glasses. The heteronuclear techniques will be supplemented by controlled-excitation for dephasing rotational amplitudes (CEDRA), and XY8-dipolar restoration at the magic angle (XY8- DRAMA), two new REDOR-like homonuclear dephasing experiments which we have introduced recently for accurate distance measurements. These pulse sequences will be used to select two or three of a cluster of stable- isotope labels to generate multiple, along-range distance measurements to characterize binding-site geometry. The sensitivity of solid-state NMR for this kind of work already has been established in practical applications on sizeable proteins. We now routinely perform long-range distance measurements on one micromole of a 5O-kD labeled protein complex. We propose specific new REDOR/TEDOR/CEDRA/DRAMA solid-state experiments to characterize: (1) EPSP synthase domain closure mi substrate binding; (2) Trp synthase indole-tunnel reorganization on serine binding; (3) Gln binding protein hinge motion on substrate binding; (4) the geometry of intact lac repressor bound to DNA; (5) the geometry of the binding site of leucine specific binding protein complexed to L-leucine; and (6) the multiple binding sites of lumazine synthase-riboflavin synthase complex. All of these practical applications could lead both to new science and new biotechnology, the latter including the use of solid-state NMR to assist in the biorational design of drugs.